Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.64   5.217%   $152.1859   $152.19   $152.20   $152.20  
  Purchase #2 $35.67   5.332%   $37.5719   $37.57   $37.55   $37.60  
  Purchase #3 $112.36   4.122%   $116.9915   $116.99   $117.00   $117.00  
  Purchase #4 $90.54   11.122%   $100.6099   $100.61   $100.60   $100.60  
  Purchase #5 $157.91   4.482%   $164.9875   $164.99   $165.00   $165.00  
  Purchase #6 $198.84   13.851%   $226.3813   $226.38   $226.40   $226.40  
  Purchase #7 $233.70   4.738%   $244.7727   $244.77   $244.75   $244.80  
  7 purchase totals = $973.66       $1,043.5007   $1,043.50   $1,043.50   $1,043.60